Piezoelectric actuator and pump using same

ABSTRACT

A method of manufacturing piezoelectric actuators ( 14 ) is disclosed along with a minimum diaphragm pump ( 10 ) using the actuators. The object was an actuator which could be used in miniature diaphragm pumps and other applications and which would be smaller in size and simpler to manufacture than prior art actuators, yet would provide forces and displacements an order of magnitude higher than any previously known devices of similar size. The pump ( 10 ) incorporates the new actuator along with a novel one-way valve ( 200 ) and a small driver circuit ( 18 ). The pump is of direct application in the liquid cooling systems of small computers, and in other fluid systems.

[0001] This application claims the benefit of U.S. Provisional PatentApplication No. 60/233,248 filed Sep. 18, 2000[Sep. 18, 2000].

TECHNICAL FIELD

[0002] The present invention is in the field of the manufacture offerroelectric actuators and miniature diaphragm pumps using theseactuators as the prime mover. In the best mode the actuators arepiezoelectric.

BACKGROUND ART

[0003] The prior art for this invention may be grouped as follows:

[0004] I. U.S. Pat. Nos. 5,471,721, 5,632,841, 5,849,125, 6,162,313,6,042,345, 6,060,811, and 6,071,087 showing either prestressing ofpiezoelectric actuators, or dome-shaped piezoelectric actuators, orboth. This prior art is generally inapposite because the presentinvention does not use a prestressed or dome-shaped piezoelectricactuator.

[0005] II. U.S. Pat. Nos. 6,179,584, 6,213,735, 5,271,724, 5,759,015,5,876,187, 6,227,809 showing so-called micropumps. Such pumps generallypump only a drop of fluid at a time; because of the small forces and lowReynolds numbers involved, this prior art is generally inapposite.

[0006] III. U.S. Pat. Nos. 4,034,780, 4,095,615 showing flapper valves.These are flappers mounted on a separate hinge. No prior art was foundshowing a flex valve with a miniature pump.

[0007] IV. U.S. Pat. Nos. 5,084,345, 4,859,530, 3,936,342, 5,049,421showing use of polyimide adhesives for various purposes, includingbonding metals and other materials to film.

[0008] V. U.S. Pat. Nos. 4,939,405, 5,945,768 showing electrical drivercircuits for piezoelectric actuators.

[0009] VI. U.S. Pat. Nos. 6,227,824, 6,033,191, 6,109,889, German WO87/07218 showing various kinds of pumps incorporating piezoelectricactuators.

DISCLOSURE OF INVENTION

[0010] This invention is a method for making a high-displacementferroelectric actuator, in this case a piezoelectric actuator. Thispiezoelectric actuator may then be used as the diaphragm in a smalldiaphragm pump. The pump is small, lightweight, quiet, and efficient.The best mode, a round pump about 40 mm[1.5″] in] diameter by about 13mm[0.5″]thick and weighing approximately 35 g [one ounce], can pumpupwards of 450 milliliters of water or other fluids per minute. Thesepumping rates are accomplished using a six-volt battery at 25 mm drivingthrough a small electronic driver circuit, approximately 25 mm [1″]square. This circuit forms part of the invention. The one way valve[s]necessary for operation of the invention are flex valves in which a thinfilm of polyimide acts as the working element.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a perspective view of the pump of the invention with theparts in the positions they would be for the best mode.

[0012]FIG. 2 is a sectional view of the pump along line 2-2 of FIG. 1.

[0013]FIG. 3 is a sectional view of the press used to make thepiezoelectric actuators of the invention.

[0014]FIG. 4 shows the driver circuit for the piezoelectric actuatorused with the pump.

[0015]FIG. 5 is a partially diagrammatic view showing an alternativeembodiment of the invention in which the pump chamber is reduced insize.

[0016]FIG. 6 is a partially diagrammatic view showing anotheralternative embodiment of a pump in which the inlet and outlet areperpendicular to the plane of the actuator.

BEST MODE FOR CARRYING OUT THE INVENTION

[0017]FIG. 1 shows how the piezoelectric actuator of the presentinvention may be used in a miniature diaphragm pump. The pump 10 isgenerally in the form of a circular short cylinder. It includes the pumpbody 12, piezoelectric actuator 14, pump cover 16 and piezoelectricactuator electronic driver circuit 18. The pump body 12 has lugs 20 formounting the pump to any substrate. Inlet 22 and outlet 24 are part ofthe pump body 12 though they could be separate pieces otherwise fastenedto the pump body. The pump cover 16 is essentially the same diameter andof the same material as the pump body 12. The material would ordinarilybe of a standard plastic such as acetal[DELRIN®], PVC, or PC, or of ametal such as stainless steel or brass. These are preferable since theycan be easily machined or thermally formed. The cover 16 may be fastenedto the pump body 12 by any means such as by a fast-curing adhesive whilethe pump body 12 and cover 16 are under compression such as by clamping.The pump cover has an opening 26 for venting the space above theactuator 14.

[0018] The dimensions of the pump depend on the particular application.In the best mode the pump body 12 is about 40 mm[1.5″] in diameter. Apump chamber 30 is formed in the center of the pump body 12, for exampleby molding or machining. The pump chamber 30 is about 28 mm[1.125″] indiameter or about 3 mm[⅛″] less in diameter than the diameter of thepiezoelectric actuator 14. The chamber 30 is about 6 mm[0.25″] deep. Aseat 32 about 3 mm[0.125″] wide and about 2 mm[0.070″] deep is providedin the pump body 12 at the top of the pump chamber 30. As shown in FIG.2 the piezoelectric actuator 14 is mounted on the seat 32 to form thediaphragm in the top of the pump chamber 30.

[0019] To assemble the pump a sealing washer 34 the same diameter as thepiezoelectric actuator is put on the seat 32 to seal the pump chamberwhen the piezoelectric actuator 14 is put in place. The sealing washer34 may be of a relatively soft material such as Buna-N or silicon rubberto account for any irregularities in the mating surfaces and ensure agood seal between the actuator 14 and the pump body 12. Once thepiezoelectric actuator 14 is in place an o-ring seal 36 is placed on topof the piezoelectric actuator 14 to hold the piezoelectric actuator 14in place and seal it from the cover 16. The cover 16 of the same outsidediameter as the pump body 12 base but only about ⅛″ thick is then put inplace. Sealing washer 34 and o-ring seal 36 are referred to collectivelyas the pump seals, even though they both have the additional function offixing the actuator 14 in place with respect to the pump body 12. Thecover 16 is then fastened to the body 12 while under compression, forexample by adhesive under clamping pressure, to seal the piezoelectricactuator 14 to the body 12 and fix the actuator 14 in place to allowpumping action.

[0020] The process for making the piezoelectric actuator 14 generally isas follows:

[0021] A piezoelectric wafer 38 formed of a polycrystallineferroelectric material such as PZT5A available from Morgan ElectroCeramics is obtained. As the name implies this material is actually aceramic. It is processed into the high displacement piezoelectricactuator 14 by laminating the piezoelectric wafer 38 between a metalsubstrate layer 40 and an outer metal layer 42 as shown in FIG. 2.,where the thicknesses of the three layers and the adhesive between themare exaggerated for clarity. The bonding agent 41 between the layers 38and 40 is a polyimide adhesive. This lamination process does severalthings: It ruggedizes the piezoelectric actuator 14 because the metallayers keep the piezoelectric from fracturing during high displacement.It permits higher voltage due to the relatively low dielectric constantof the polyimide adhesive, thereby allowing 3-5 times higherdisplacement than a conventional piezoelectric. Being laminated betweenmetal layers using a high performance polyimide adhesive makes thepiezoelectric actuator highly resistant to shock and vibrations. Withthis invention piezoelectric actuator devices can be used inenvironments as hot as a continuous 200° C., compared to only 115° C.for a conventional piezoelectric. The significant increase intemperature is due to the polyimide adhesive used in the bonding processwhich is unaffected by temperatures up to 200° C. Epoxy adhesives usedin conventional piezoelectrics normally can withstand temperatures up toonly 115° C. This increase in operating temperature would allow thepumps of this invention to be used in a variety of pump applications,even pumping boiling water continuously.

[0022] The piezoelectric wafers 38 are available from the vendormentioned in various shapes and thicknesses. For the invention circularwafers 25 mm[1″] in diameter and 0.2 mm[0.008″] thick were found to beoptimum. Square wafers were tried but did not give maximum displacement.In general the thinner the wafer, the greater the displacement at agiven voltage, but the lower the force. The 0.2 mm[8-mil] thicknessgives the best flow rate for the diameter of the wafer.

[0023] In the best mode stainless steel 0.1 mm[0.004″] thick is used forthe substrate layer 40, the layer in contact with the pumped liquid.Stainless steel is chosen for its compatibility with many liquids,including water, its fatigue resistance, its electrical conductivity andits ready availability at low cost. Aluminum 0.05 mm[0.001″] thick isused for the outer layer 42 primarily for its electrical conductivity intransmitting the actuating voltage to the piezoelectric wafer 38 acrossits surface, but also for its robustness and ready availability at lowcost.

[0024] The diameter of the piezoelectric wafer 38 being about 25 mm[1″]as noted above, the diameter of the substrate layer 40 is about 40mm[1.25″]. The setback of the wafer 38 from the edge of the substratelayer 40 is an important feature of the invention. This leaves a rimthat serves as a clamping surface for the actuator assembly. This meansthat the entire piezoelectric wafer 38 is free and relativelyunconstrained, except insofar as it is bonded to the substrate 40 andthe outer layer 42. This allows maximum displacement of the actuator 14,ensuring maximum flow of liquid through the pump.

[0025] The diameter of the outer layer 42 is smaller than the diameterof the wafer 38. This setback of the outer layer 42 from the edge of thewafer 38 is done to prevent arcing over of the driving voltage from theouter layer 42 to the substrate layer 40.

[0026] Other materials and thicknesses may be used for the enclosinglayers 40 and 42 as long as they meet the requirements noted.

[0027] Of special note is that the piezoelectric actuator of theinvention is flat. In much of the prior art the actuator is dome-shaped,it being supposed that this shape is necessary for maximum displacementof the actuator and therefore maximum capacity of the pump for a givensize actuator. Special molds and methods are proliferated to produce theshapes of the actuator considered necessary, or to produce a prestressin the actuator that is supposed to increase its displacement. Our testsof the invention have shown, however, that a dome shape is notnecessary, and that the flat actuator has a higher pumping capacity fora given size than any known pump in the prior art. As such the actuatoris much simpler to produce in large quantities, as the following willdemonstrate. The flat shape also means that the pump may be smaller fora given application. A flat actuator is also inherently easier to mountin any given application than a dome shaped actuator would be.Furthermore, pumps using the actuator have been shown to havesufficiently long life for numerous applications. Many manufacturerswhose names are household words are using or testing this invention.

[0028] The process for making the piezoelectric actuator 14 specificallyis as follows:

[0029] 1. The piezoelectric wafer 38 and and enclosing layers 40 and 42are cleaned using a solvent that does not leave a residue, such asethanol or acetone. All oil, grease, dust and fingerprints must beremoved to ensure a good bond.

[0030] 2. The piezoelectric wafer 38 is then coated on both sides with athin layer 41, not more than 0.1 mm[0.005″], of a high performancepolyimide gel adhesive such as that available from Ranbar Inc. The gelshould contain a minimum of 25% solids to allow sufficient material fora good bond after the solvent is driven off

[0031] 3. The piezoelectric wafer 38 is then placed under a standardheat lamp for about 5 minutes to remove most of the solvent from the geland start the polyimide gel polymerization process. Both sides of thepiezoelectric must be cured under the heat lamp since both sides are tobe bonded to metal.

[0032] 4. Once the adhesive is dry to the touch, the piezoelectric wafer38 is then placed between the substrate layer 40 and the outer layer 42.

[0033] 5. The assembly is placed in a special press. This press wasdeveloped specifically for making piezoelectric actuators 14 andprovides uniform temperature and pressure to ensure a good bond betweenthe three components of the actuator. Referring to the best mode shownin FIG. 3 the press comprises two 300 mm[12″]square by 6 mm[¼″] thickplates of aluminum 101 held together with thumbscrews 102, four on eachedge. To ensure uniform pressure while in the press, the bottom plate101 of the press is covered with a sheet of low cost polyimide film 104such as Upilex available from Ube Industries Ltd. The piezoelectricactuators 38 are placed on the film and a sheet of high temperature, 4mm[⅛″] thick rubber 106 is placed over the piezoelectric actuators. Therubber on top and the film on bottom cushion the piezoelectric actuators38 providing even distribution of pressure when the press is taken totemperature. Of course other dimensions of the press plates arepossible.

[0034] 6. Once the piezoelectric actuators are placed in the press thethumbscrews 102 are made finger tight.

[0035] 7. The press is then placed in a standard convection oven forthirty minutes at about 200° C.

[0036] 8. The press is removed from the oven, allowed to cool to a safetemperature, and the actuators 14 removed from the press.

[0037] The press 100 is the result of an effort to develop a low cost,rapid process for manufacturing piezoelectric actuators. The press takesadvantage of the thermal expansion of the aluminum plates 101 whichcreates the necessary pressure to cause the polyimide adhesive to bondto the piezoelectric wafer 38 and metal layers 40, 42 while it is atcuring temperature. The press can be put into the oven, and taken out,while the oven is at temperature thereby allowing continuous operationduring the manufacturing process. The abrupt change in temperature doesnot affect the piezoelectric actuators 14 since they will remain underpressure even while the press is removed from the oven and allowed toassume room temperature.

[0038] Of special note is that this press process is one of furtherdriving off the solvent and curing the polyimide at a relatively lowtemperature. Prior art processes for making similar piezoelectricactuators require the mold/press to be taken to much highertemperatures, high enough to melt the polyimide adhesive. Furthermore,since such high temperatures depole the piezoelectric ceramic, it isnecessary to pole it again at the end of the process. The presentinvention eliminates this step altogether, thus contributing to thelower cost of manufacturing the piezoelectric actuators.

[0039] Using these simple methods and hardware it is possible tomanufacture hundreds of thousands of piezoelectric actuators 14 permonth, or even more, depending on the scale of the operation desired.

[0040] The principle of the piezoelectric actuator pump 10 is the sameas for any diaphragm pump. Normally the diaphragm in a diaphragm pump isoperated by a cam or a pushrod connected to a motor or engine. This isnot the case in the piezoelectric actuator pump 10. The piezoelectricactuator 14 acts as the diaphragm and moves when a pulsed electric fieldis imposed across the piezoelectric wafer 38 by means of the enclosinglayers 40 and 42. This varying electric field causes the piezoelectricactuator 14 to expand and contract. As the actuator 14 expands, with itsedge constrained, it assumes a slight dome shape as the center of theactuator moves away from the pump chamber 30. This draws liquid into thepump chamber 30 through the inlet 22. When the piezoelectric actuator 14contracts it moves toward the liquid, forcing it out of the pump chamber30 through outlet 24.

[0041] One of the problems with prior art piezoelectric actuators hasbeen the voltage necessary to drive the piezoelectric. To provide powerto the piezoelectric actuator pump 10 the electrical driver 18 shown inFIG. 4 was invented that converts the voltage from any six volt d.c.power source to an alternating current of over 200 volts peak-to-peak.This voltage is sufficient in the preferred embodiment to drive apiezoelectric actuator to attain the pumping rates noted above. In thecircuit in FIG. 4 point A is connected to the substrate layer 40 whilepoint B is connected to the outer layer 42.

[0042] Piezoelectric actuators perform better when the peak-to-peakvoltage is not evenly balanced. They respond better to a positivevoltage than the same negative voltage. Thus the circuit 18 has beendesigned to produce alternating current with the voltage offset to 150volts positive and 50 volts negative. This is sufficient voltage for thepiezoelectric actuator to make a very efficient pump. While a sinusoidalwave will work, at the lower frequencies and voltages, a square wavemakes the piezoelectric more efficient. Values of the circuit componentsin FIG. 4 are as follows: R1 8 to 20 MΩ R2 8 to 20 MΩ R3  680 KΩ R4   1MΩ C1  0.1 μF C2  0.1 μF C3  0.1 μF[200 v] C4 0.47 μF[200] L1  680 μH D1BAS21 diode

[0043] U1 is an IMP 528 chip designated an electroluminescent lampdriver. In this circuit, with the other components, it serves to shapethe pulses and amplify them to the 200 volt peak-to-peak value needed todrive the piezoelectric actuator 14. The values of R1 and R2 are chosento vary the frequency of the output between about 35 Hz and about 85 Hz,depending on the particular application.

[0044] This circuit is composed of miniaturized components so it may becontained in a box 302 approximately 25 mm[1″] square by 6 mm[¼″] deep.It has only eleven off-the-shelf surface mount components. The box 302may be mounted anywhere in proximity to the pump 10. In the best mode itis mounted on top of the pump, as shown in FIGS. 1 and 2, for example byan appropriate adhesive. Leads 15 run from the driver circuit 18 and arefastened to spring loaded contacts 304 such as those sold by the ECTCompany under the trademark POGO®. These contacts 304 are mounted in abox 306 on top of pump cover 16 and project through the pump cover 16 tomake contact with the two layers 40 and 42. This small driver circuiteliminates the need for the large power supplies and transformers usedin prior art piezoelectric applications. Alternatively the leads 15could be run through an opening in the cover 16 and fastenedelectrically to the layers 40 and 42, as by soldering. O-ring 36 is softenough to accommodate the soldered point on the substrate layer 42.

[0045] Several conventional types of one-way valves were evaluated asinlet and outlet valves for the piezoelectric actuator pump 10. All hadvarious drawbacks including bulk and poor response to the dynamicbehavior of the piezoelectric actuator 14. An inline flex valve 200 wasinvented that is well adapted to the action of the piezoelectricactuator 14 as shown in FIG. 2. The working element of the flex valve isan elliptical disk 202 of polyimide film about 0.05 mm[0.002″] thick.The disk 202 is the same size and shape as the end of a short piece ofrigid tube 204 formed at about a 45° angle to the axis of the rigid tube204. The inside diameter of the rigid tube 204 is the same as the insidediameter of the inlet 22 or outlet 24 of the pump body 12. Rigid tube204 is captured in the end of the flexible system conduit 206 whichslips over the inlet/outlet 22,24 and carries the system liquid, asshown in FIG. 2. Valve disk 202 is attached to the nether end of theslanted surface at the point designated 203 by any sufficient means suchas by adhesive or thermal bonding. A similar flex valve 200 may beplaced in the outlet 24. Both disks 202 of both valves would point inthe same direction downstream. However, it was found in operating thepump 10 that it would pump at full capacity with no valve at all in theoutlet. It is postulated that the liquid in the inlet circuit, even withthe inlet valve partially open, provides enough inertia to act as aclosed inlet valve. Operation with only the inlet valve is considered tobe the best mode.

[0046] This flex valve 200 is an important feature of the invention. Itis of absolute minimum bulk. The mass of the disk 202 is also about aslight as it could possibly be so it reacts rapidly to the action of theactuator 14. When it is open it presents virtually no resistance to thesystem flow. Mounted at the 45° angle, it has to move through an angleof only 45° to fully open, whereas if it were mounted perpendicular tothe flow it would have to move through an angle twice as large. It is ofextreme simplicity and low cost of materials and fabrication. Also nopart of the valve 200 projects into pump chamber 30. This minimizes thevolume of pump chamber 30 which helps make the pump self-priming andincreases its efficiency. Further contributing to these characteristicsis that the flex valve 200 is biased closed when the pump is notoperating.

[0047]FIGS. 5 and 6 show alternative embodiments of the pump of theinvention. The pump in FIG. 5 is essentially the same as that of FIG. 2except that the pump chamber 30 is reduced in thickness to that of thesealing washer 34. This improves the self-priming ability of the pump.The pump in FIG. 6 also has a minimally thick pump chamber 30. Further,the inlet 22 and outlet 24 are perpendicular to the plane of theactuator 14, a configuration that may be more convenient in someapplications.

[0048] In yet another embodiment, not shown, the bottom of the pump bodycomprises a piezoelectric actuator 14 arranged identically but as amirror image of the piezoelectric actuator 14 just described, with thesubstrate layers 40 facing each other across the pump chamber 30.

[0049] In still another embodiment, not shown, two of the pumps abovedescribed are mounted side by side in one pump body. The actuator;seals; inlets and outlets, with one-way valve in the inlets only; pumpcovers; and drivers are positioned in one or more of the configurationsdescribed above. In a preferred form of this embodiment, the drivers arein series electrically, with the pumps operating in parallel fluidwisein the system in which they are deployed.

INDUSTRIAL APPLICABILITY

[0050] This invention has particular application for water cooling ofthe CPU in computers but may have wider applications wherever a verysmall pump of relatively high flow rate and minimum power consumption isneeded to move liquids at very low cost. The piezoelectric actuator byitself can have very many other applications, such as speakers, audiblealarms, automotive sensors, sound generators for active noisecancellation, and accelerometers.

1. [Amended] The method of making piezoelectric actuators 14 frompiezoelectric wafers 38 wherein the improvement comprises the steps of:a. cleaning the piezoelectric wafer 38 and enclosing metallic layers 40and 42 using a solvent that does not leave a residue; b. coating bothsides of the piezoelectric wafer 38 with a thin layer, not more than0.01 mm[0.005″], of a high performance polyimide gel adhesive 41, thegel containing a minimum of 25% solids to allow sufficient material fora good bond after the solvent is driven off; c. placing both sides ofthe piezoelectric wafer 38 under a standard heat lamp for about fiveminutes to remove most of the solvent from the gel and start thepolyimide gel polymerization process; d. once the adhesive is dry to thetouch, placing the piezoelectric wafer 38 between the metallic layers 40and 42 to form a piezoelectric actuator 14; e. assembling a presscomprising two 300 mm[12″] square by 6 mm[¼″] thick plates of aluminum101 held together with thumbscrews 102, at least two on each edge,covering the bottom plate 101 of the press with a sheet of polyimidefilm 104, placing multiple piezoelectric actuators 14 on the film andcovering with a sheet of high temperature 3 mm[⅛″] thick rubber 106; f.making the thumbscrews 102 finger tight; g. placing the press 100 in astandard convection oven for about thirty minutes at about 200° C.; h.removing the press 100 from the oven, allowing it to cool to a safetemperature, and removing the actuators 14 from the press.
 2. [Amended]A miniature diaphragm pump 10 for pumping fluids wherein the improvementcomprises: a pump body 12 having a pump chamber 30, an inlet 22, and anoutlet 24; a cover 16 for the pump body 12; a piezoelectric actuator 14fixed between the pump body 12 and the cover 16 as a diaphragm; aone-way valve 200 located in one or both of the inlet 22 and the outlet24 so that no part of the valve 200 protrudes into pump chamber 30; andan electrical driver circuit 18 for the piezoelectric actuator 14located in proximity to the pump
 10. 3. The pump 10 of claim 2 furthercharacterized in that the piezoelectric actuator comprises a layer ofpiezoelectric ceramic 38 between a substrate layer 40 of a first metaland an outer layer 42 of a second metal and bonded to each by anadhesive 41 in a press 100 at a temperature of about 200° C.
 4. The pumpof claim 3 further characterized in that the substrate layer 40 is ofstainless steel and the outer layer 42 is of aluminum.
 5. The pump ofclaim 4 further characterized in that the adhesive 41 is a polyimide. 6.The pump of claim 5 further characterized in that the piezoelectricactuator 14 is flat.
 7. The pump of claim 6 further characterized inthat the press 100 comprises flat plates.
 8. [Amended] The pump of claim7 further characterized in that the piezoelectric actuator 14 is made bythe following process: a. clean a piezoelectric wafer 38 and enclosingmetallic layers 40 and 42 using a solvent that does not leave a residue;b. coat both sides of the piezoelectric wafer 38 with a thin layer, notmore than 0.005″, of a high performance polyimide gel adhesive 41containing a minimum of 25% solids to allow sufficient material for agood bond after the solvent is driven off; c. place both sides of thepiezoelectric wafer 38 under a standard heat lamp for about five minutesto remove most of the solvent from the gel and start the polyimide gelpolymerition process; d. once the adhesive is dry to the touch, placethe piezoelectric wafer 38 between the metallic layers 40 and 42 to froma piezoelectric actuator
 14. e. assemble a press 100 comprising two 12″inch square by ¼″ thick plates of aluminum 101 held together withthumbscrews 102, at least two on each edge, cover the bottom plate 101of the press 100 with a sheet of polyimide film 104, place multiplepiezoelectric actuators 14 on the film and cover with a sheet of hightemperature ⅛″ rubber sheet 106; f. make the thumbscrews 102 fingertight; g. place the press 100 in a standard convection oven for aboutthirty minutes at approximately 195° C.; h. remove the press 100 fromthe oven, allow it to cool to a safe temperature, and remove theactuators 14 from the press.
 9. The pump 10 of claim 8 furthercharacterized in that the pump body 12, cover 16, and piezoelectricactuator 14 are round and the piezoelectric actuator 14 is held in placebetween the pump body 12 and cover 16 by an o-ring 36 compressed betweenthe cover 16 and the piezoelectric actuator 14, a plastic sealing washer34 being interposed between the piezoelectric actuator 14 and the pumpbody
 12. 10. The pump 10 of claim 9 further characterized in that thepump chamber 30 is only as deep as the thickness of the sealing washer34.
 11. The pump 10 of claim 9 further characterized in that the axes ofthe inlet 22 and outlet 24 are essentially perpendicular to the side ofthe pump body
 12. 12. The pump 10 of claim 9 further characterized inthat the axes of the inlet 22 and outlet 24 are essentiallyperpendicular to the plane of the piezoelectric actuator
 14. 13. Thepump 10 of claim 11 further characterized in that the substrate layer 40faces the pump chamber
 30. 14. The pump 10 of claim 13 furthercharacterized in that the piezoelectric ceramic layer 38 is smaller indiameter than the substrate layer 40 and the outer layer 42 is smallerin diameter than the piezoelectric ceramic layer
 38. 15. The pump 10 ofclaim 14 further characterized in that the compressed o-ring 36 actsonly on the substrate layer 40 to fix the piezoelectric actuator 14 inplace in the pump body
 12. 16. The pump 10 of claim 15 furthercharacterized in that the one-way valve 200 comprises a length of rigidtubing 204 connected to the inlet 22 or outlet 24, with one end of therigid tubing 204 at an approximate 45° angle with the axis of the rigidtubing 204 forming a slanted surface, and a thin disk 202 the same sizeand shape as the slanted surface affixed to the nether end 203 of theslanted surface acting as the working element of the one-way valve 200.17. The pump 10 of claim 16 further characterized in that the thin disk202 comprising the working element of the one-way valve 200 is formed ofpolyimide film.
 18. The pump 10 of claim 17 further characterized inthat a one-way valve 200 is located in both the inlet 22 and the outlet24.
 19. The pump 10 of claim 17 further characterized in that a one-wayvalve 200 is located only in the inlet
 22. 20. The pump 10 of claim 19further characterized in that no part of the one-way valve 200 islocated in the pump chamber
 30. 21. A pump 10 according to claim 20further characterized in that the electrical driver for thepiezoelectric actuator 14 comprises a 6-volt-d.c. power source and acircuit 18 for converting the 6-volts-d.c. to an a.c. voltage sufficientto drive the piezoelectric actuator 14 to a pumping condition.
 22. Apump according to claim 21 further characterized in that the electricaldriver comprises the circuit 18 shown in FIG.
 4. in which point A isconnected to the substrate layer 40 of the piezoelectric actuator 14 andpoint B is connected to the outer layer 42 of the actuator 14; in whichthe elements have the following values: R1 8 to 20 MΩ R2 8 to 20 MΩ R3 680 KΩ R4   1 MΩ C1  0.1 μF C2  0.1 μF C3  0.1 μF[200 v] C4 0.47μF[200] L1  680 μH D1 BAS21 diode

and in which U1 is an IMP 528 chip designated an electroluminescent lampdriver and the values of R1 and R2 are chosen to vary the frequency ofthe output between about 35 Hz and about 85 Hz.
 23. The pump 10 of claim22 in which a square wave waveform is produced by the electrical drivercircuit 18 of approximately 150 volts positive and 50 volts negativeamplitude.
 24. The pump 10 of claim 23 further characterized in that theelectrical driver consists of miniaturized circuit elements and iscontained in a box 302 mounted on the pump cover
 16. 25. The pump 10 ofclaim 24 further characterized in that the output of the electricaldriver circuit 18 is connected to the piezoelectric actuator 14 by meansof spring loaded contacts 304 projecting through the pump cover
 16. 26.The pump 10 of claim 25 further characterized in that two identicalactuators 14 are positioned on either end of the pump body, thesubstrate layers 40 of each actuator 14 facing each other across thepump chamber
 30. 27. The pump 10 of claim 25 further characterized inthat two pump chambers 30 with associated piezoelectric actuators 14,inlets 22 and outlets 24, with one-way valves 200 in the inlets 22 only;seals 34,36; pump covers 16; and drivers 18 are positioned side by sidein one pump body, the two drivers 18 being in series electrically withthe piezoelectric actuators 14 and operating in parallel fluidwise. 28.A miniature diaphragm pump 10 for pumping fluids wherein the improvementcomprises; a pump body 12 generally in the form of a disk measuring fromabout an inch to about an inch and a half across and from about aquarter inch to five-eighths inch thick with a generally circular pumpchamber 30, and at least one opening in the pump body acting as an inlet22 or outlet 24 and connected to a fluid system conduit 206; apiezoelectric actuator 14 serving as the diaphragm of the pump 10, theactuator 14 being generally circular in shape and essentially flat andhaving been made of two metallic layers 40,42 sandwiching a layer ofpiezoelectric ceramic 38, the three layers being bonded together by apolyimide adhesive 41 in a flat press 100 at a temperature of about 200°C.; a pump cover 16; the piezoelectric actuator 14 being sealed and heldin place between the pump body 12 and the pump cover 16 by a sealingwasher 34 and an o-ring seal 36, the pump cover 16 being fastened to thepump body 12 while under compression; a one-way valve 200 positioned inthe inlet 22 to allow flow of system fluid only into the pump 10, thevalve 200 comprising a length of rigid tubing 204 with one end formed atabout a 45° angle to the axis of the tubing 204 and comprising a slantedend surface, with an elliptical disk 202 of polyimide film the same sizeand shape as the slanted end surface attached to the slanted end surfaceat the nether end 203 thereof, the valve 200 being mounted in the systemconduit 206; an electrical driver circuit 18 for the piezoelectricactuator 14 contained in a box 302 generally smaller in size than thepump body 12 mounted in proximity to the pump 10 and connectedelectrically to the piezoelectric actuator 14, the piezoelectric drivercircuit 18 containing an integrated circuit device constituting anelectroluminescent lamp driver, the piezoelectric driver circuit 18producing a square wave of 150 volts positive to 50 volts negativeacross the piezoelectric actuator 14.